A good primer on glass fibre reinforcement of polypropylene is the article, "The Effects of Glass Fibre Size and Coupling Additives on the Properties of Glass Fibre Reinforced Polypropylene," PPG/Silenka Information, pp. 7-12, (October 1990). This article points out that glass fibre reinforcement of polypropylene can lead to improvements in tensile, flexural and impact strengths.
In addition, several factors influence the degree of improvement in these properties including the melt flow index of the polymer during processing with the glass fibre, the amount and type of coupling agent employed, the amount of glass employed, whether the materials are compounded in one processing step or in two or more processing steps and the presence or absence of an initiator during processing.
The article points out that typical coupling agents are (co)polymers which contain carboxyl groups. There are numerous additives for this purpose on the market. However, these coupling agents, while improving the adhesion between the polypropylene and the glass fibre, may not have a positive influence on the melt flow index during processing and/or on the end properties of the polypropylene. In particular, the coupling agent generally makes up about 10% by weight of the polypropylene composition and, since it is distributed throughout the composition, it can detrimentally effect one or more properties of the polypropylene.
The article also points out that other coupling agents such as the bismaleimides and the maleic acid anhydride and 4,4'-diaminodiphenylmethane in combination, may be employed. With the latter coupling agent, peroxide initiators may be employed to further improve the glass reinforced polypropylene properties. The article does not suggest the use of a peroxide initiator alone for improving the properties of glass fibre reinforced polypropylene.
There are a number of publications which describe the treatment of propylene (co)polymers with peroxides, albeit generally with different goals in mind. For instance, such references generally refer to a degradation or cross-linking of the propylene (co)polymers and degradation normally predominates. Generally, such peroxide treatments lead to a polypropylene with a narrow molecular weight distribution and having both lower number average and weight average molecular weights. A typical example of such publications is, "Degradation of Polyolefins during Melt Processing," Hinsken et al., Polymer Degradation and Stability, 34, pp. 279-293 (1991).
Canadian patent 999,698 discloses the degradation of polypropylene in a nitrogen atmosphere at 150.degree.-220.degree. C. by using organic peroxides such as t-butyl peroxymaleic acid and 2,5-bis(t-butylperoxy)-2,5-dimethyl hexane, among others. This modification process leads to a controlled reduction of at least 50% in the viscosity (an increase in the melt flow index (MFI)) of the polypropylene and thus significant degradation of the polypropylene. This degraded polypropylene is for use in hot melt adhesives wherefor, in general, amorphous atactic polypropylene is most suitable.
Netherlands patent application 6,808,574 discloses the modification of rubbers, including ethylene/propylene rubbers, by contacting the rubbers with a peroxide such as t-butyl peroxy crotonate or di-t-butyl-di-peroxy fumarate at a temperature of 140.degree.-160.degree. C. in order to crosslink the rubber composition.
In addition, the following patent publications disclose the modification of polypropylene with unsaturated peroxides: International patent applications WO 91/00301, WO 91/00300 and European patent applications 0 208 353, 0 273 990, and 0 322 945. In each case, the polypropylene is degraded resulting in a lower final weight average molecular weight, although, with the addition of unsaturated co-crosslinking agents, a cross-linked polypropylene with a higher molecular weight can be obtained.
Finally, Belgian patent publication 815,357 teaches the degradation of polypropylene with peroxides in an oxygen atmosphere. Unsaturated peroxides are not mentioned in this publication and the goal is to significantly reduce the molecular weight of the polypropylene.
It is the primary object of the present invention to modify (co)polymers in order to introduce an adhesion promoting functional group therein. It is a further object of the present invention to improve the properties of (co)polymers which are reinforced with polymer reinforcing materials. It is a still further object of the present invention to provide an improved process for the reinforcement of (co)polymers. These and other objects of the invention will be apparent from the description which follows.